Your Comprehensive Guide to Water-Soluble Vitamins: Vitamin C and the B-Complex

The category of any vitamin is done according to their solubility. Most of the vitamins are soluble in water and hence are known as water-soluble vitamins. However, there are some vitamins which are fat soluble meaning that they dissolve in fat or oil. There are only four fat soluble vitamins. Whereas, there are about nine water-soluble vitamins that are present in our human diet. These water-soluble vitamins are: vitamin B1 (thiamine); vitamin B2 (riboflavin); vitamin B3 (niacin); vitamin B5 (pantothenic acid); vitamin B6; vitamin B7 (biotin); vitamin B9; vitamin B12 (cobalamin) and vitamin C.

Water-soluble vitamins, unlike the fat-soluble vitamins, are usually not stored in the body and this is why one needs to get them from the diet on a regular basis (1).

In this article, we will talk about water-soluble vitamins, what role they play in the body and their benefits along with dietary sources.

Also known as thiamine, vitamin B1, was the first water-soluble vitamin to be scientifically known (1).

There are many types of this vitamin such as:

• Thiamine Pyrophosphate: This type of vitamin B1 is also known as thiamine pyrophosphate or thiamine diphosphate and it is present in great amount in the body and is also the primary type of this vitamin present in whole foods.
• Thiamine Triphosphate: This type of vitamin B1 is in foods that are animal-sourced and is found in lesser amount than thiamine pyrophosphate.
• Thiamine Hydrochloride: This is a synthetic and standard type of vitamin B1 used in supplements.
• Thiamine Mononitrate: This is also a synthetic type of vitamin B1 added to processed food or animal feed.

Just like the other B vitamins, vitamin B1 acts as a coenzyme in the body and this is applicable to all its active forms; however, thiamine pyrophosphate is the most important one. Vitamin B1 has an important role in various chemical reactions, such as it helps support sugar formation and helps in converting the nutrients into energy form (1).

Some of the richest dietary sources of vitamin B1 consist of thiamine seeds, nuts, liver, whole grains and pork. Whereas, vegetables fruits and dairy products often do not provide enough of vitamin B1.

Vitamin B1 deficiency is not that common, however, increased levels of blood sugar can increase the secretion of vitamin B1 through urine, thus causing deficiency or the risk of deficiency. People suffering from type 1 and type 2 diabetes will often have reduced levels of vitamin B1 by about 75 to 76% (1).

Alcoholics are also at increased risk for vitamin B1 deficiency as they will have impaired thiamine absorption and because of poor diet (4).

Serious vitamin B1 deficiency can cause disorders, such as Wernicke-Korsakoff syndrome and beriberi. These disorders are also present with a myriad of symptoms, such as weight loss, anorexia, mental issues, heart enlargement, muscle weakness and impaired neural function (1).

Thiamine or vitamin B1 is considered safe and as of now there are no reports of any adverse side effects after consuming large quantities of this vitamin in the form of supplements or foods. This is in part due to excretion of any excess thiamine present in the body in urine form.

This is why a tolerable upper intake level for vitamin B1 is not established; however, it does not mean that one can take it in high amounts without any consequences, as it does not exclude the possibility of toxicity at very high amounts of vitamin B1.

There is no sufficient evidence that thiamine supplements are beneficial to healthy individuals who meet their daily vitamin B1 requirements from food. However, diabetics and people with insufficient vitamin B1 can benefit a lot from taking high-dose vitamin B supplements to help reduce their blood pressure as well as blood sugar (5).

Reduced intake of vitamin B1 is also linked with disorders, such as fibromyalgia, glaucoma and depression. However, there is more evidence needed before coming to any concrete conclusions about this (6, 7).

Riboflavin is the only water-soluble vitamin that is utilized as a food coloring and its name flavus means “yellow” in Latin.

Flavoproteins are the dietary substances which release riboflavin during process of digestion. Flavin adenine dinucleotide and flavin mononucleotide are the two of the most common flavoproteins which are present in a variety of foods.

Riboflavin acts coenzyme in different chemical reactions. Just like vitamin B1, Vitamin B2 also plays a role in transforming the nutrients into energy and is also needed for the conversion of tryptophan to vitamin B3 (niacin) and conversion of vitamin B6 to its active form.

Some of the richest dietary sources of vitamin B2 are leafy vegetables, eggs, broccoli, legumes, milk, meat, mushrooms and Yeast extract spread. Riboflavin or vitamin B2 is also used as a yellow-orange food coloring and added to processed breakfast cereals.

It is rare to find vitamin B2 or riboflavin deficiency in developed countries. However, in case of old age, poor diet, alcoholism and lung diseases all these can increase the risk of vitamin B2 deficiency. Severe deficiency of this vitamin can cause ariboflavinosis, a condition characterized by inflamed tongue, sore throat, anemia; and eye and skin problems. Vitamin B2 deficiency also hinders the conversion of tryptophan to niacin and the metabolism of vitamin B6.

There have been no known side effects or toxicity reported from increased intake of supplemental or dietary riboflavin (vitamin B2). When taken in high doses, the efficacy of absorption of vitamin B2 reduces. Due to this the safe upper intake level of vitamin B2 is not established.

Healthy individuals who get their vitamin B2 from food do not benefit from taking additional supplements. However, taking low-dose vitamin B2 supplements can potentially help in lowering blood pressure and also cuts down the risk of heart disease in people who have a family history of it. This is achieved by reducing the increased homocysteine levels in individuals having two copies of the gene MTHFR 677TT ⁽⁸⁾. Increased doses of vitamin B2, like about 200 mg twice a day, can also help in decreasing migraines ⁽⁹⁾.

Vitamin B3, also commonly known as niacin, is the only B vitamin which the body can produce from another nutrient, which is tryptophan, an amino acid.

Vitamin B3 comprises of group of related nutrients and its most common forms consist of:

• Nicotinic Acid: This form is most commonly found in supplements and also present in both animal and plant-sourced foods. Increased doses of nicotinic acid supplements can cause niacin flush.
• Niacinamide (Nicotinamide) is present in foods as well as supplements.
• Nicotinamide riboside is a compound that also has vitamin B3 activity and is found in trace amounts in baker’s yeast and whey protein ⁽¹⁰⁾.

All dietary forms of vitamin B3 in the end are converted into nicotinamide adenine dinucleotide phosphate (NADP+) or nicotinamide adenine dinucleotide (NAD+) that act as coenzymes. This form of vitamin B is also an antioxidant that acts as a coenzyme in the body and is essential for function of the cells. The primary function of vitamin B3 is to generate glycolysis, which is a metabolic process that extracts energy from glucose.

Niacin or vitamin B3 is present in plants as well as animals. Some of the best sources of vitamin B3 is yeast extract spread, which contains around 128 mg in every 100 g. Other good sources of vitamin B3 are chicken, fish, dairy, products, eggs and mushrooms. Moreover, the body can manufacture this vitamin from tryptophan, which is an amino acid. According to experts, about 60 mg of tryptophan can be utilized to make 1 mg of niacin or vitamin B3 ⁽¹¹⁾.

Vitamin B3 deficiency is known as pellagra and is rare in developed countries. Pellagra is characterized by skin inflammation, mouth sores, insomnia, dementia and diarrhea. Without treatment, pellagra can be life threatening. The good news is one can easily get this vitamin from consuming various foods. Developing countries will have more vitamin B3 deficiency as people living there tend to consume food which lacks in diversity.

Following a high-protein diet can help in preventing deficiency of niacin or vitamin B3 as the body can manufacture this from the amino acid tryptophan ⁽¹²⁾.

Consuming naturally present vitamin B3 does not cause any adverse effects. However, taking high supplemental doses of vitamin B3 can cause nausea, niacin flush, vomiting, irritation of the stomach lining and liver damage. Immediate-release nicotinic acid supplements can cause niacin flush, as its side effect and it is characterized by a flush in the neck, face, chest and arms ⁽¹³⁾. Liver damage can occur with consuming extremely high doses like 3 to 9 g in a day for long-term in sustained-release or nicotinic acid in slow-release ⁽¹⁴⁾. Also, taking niacin supplements for a long period of time can increase blood sugar levels and insulin resistance ⁽¹⁵⁾.

Vitamin B3 supplements at varying doses of 1,300 to 2,000 mg per day are given to normalize the blood lipid levels ⁽¹⁶⁾.

Vitamin B5 or Pantothenic acid is present in almost all food items.

There are various types of vitamin B5 or pantothenic acid or compounds, which release the active form of this vitamin when consumed. Some of these compounds consist of:

• Coenzyme A: This is a common source of the vitamin B5 present in food items and releases pantothenic acid in the GI tract.
• Calcium Pantothenate: This is the most common type of pantothenic acid found in supplements.
• Acyl Carrier Protein: This is also present in foods and releases pantothenic acid upon digestion.
• Panthenol: This is another type of pantothenic acid commonly used in supplements.

Pantothenic acid or vitamin B5 plays an important role in various metabolic functions. It is needed for formation of coenzyme A, which is vital for the synthesis of amino acids, fatty acids, neurotransmitters, steroid hormones and other important compounds.

This vitamin is present in almost all food items. Some of the rich sources of vitamin B5 consist of yeast extract spread, caviar, shiitake mushrooms, chicken, kidneys, egg yolks and beef. There are many plant foods that are also good sources for vitamin B5, such as whole grains, root vegetables, broccoli and tomatoes.

It is very rare to find deficiency of vitamin B5 owing to its presence in almost all the food items. Vitamin B5 deficiency is seen only in cases of severe malnutrition. However, diabetic people and those who consume excessive alcohol may need higher doses of this vitamin.

There are no known adverse effects of vitamin B5 known at high doses and its tolerable upper limit is not set as of yet. However, people taking high doses, such as 10 g per day can experience diarrhea and digestive discomfort ⁽¹⁷⁾.

People who get adequate amount of vitamin B5 from their diets have not had any known benefits from pantothenic acid supplements.

Vitamin B6 is a collection of nutrients which are needed for the synthesis of a coenzyme known as pyridoxal phosphate, which is involved in more than 100 various metabolic processes.

Vitamin B6, just like other B vitamins, is a family of related compounds like:

• Pyridoxine: This form of vitamin B6 is present in vegetables, fruits and grains, as well as supplements. It can be added to processed foods.
• Pyridoxamine: According to FDA, pyridoxamine is now considered as a pharmaceutical drug. It is a common form of vitamin B6 in foods that are animal-sourced.
• Pyridoxal: Pyridoxal phosphate is the primary form of vitamin B6 in foods that are animal-sourced. All dietary forms of vitamin B6 are converted into pyridoxal 5-phosphate in the liver, which is the active form of this vitamin.

Vitamin B6 also acts as a coenzyme in various chemical reactions. Vitamin B6 is involved in formation of red blood cells and energy and metabolism of amino acids. This vitamin is needed for release of glucose from glycogen. Vitamin B6 also supports white blood cells formation and helps the body in synthesizing different types of neurotransmitters.

Vitamin B6 is found in all types of foods. Some of the excellent sources of vitamin B6 include tuna, turkey, pork, chickpeas, bananas and potatoes. Additionally, this vitamin is also added to soy-based meat substitutes and breakfast cereals. Vitamin B6 is higher in animal-sourced foods than plant foods ⁽¹⁸⁾.

It is rare to see Vitamin B6 deficiency and alcoholics are at increased risk for this Vitamin B6 deficiency ⁽¹⁹⁾. Common symptoms of Vitamin B6 deficiency consist of skin rashes, anemia, depression, confusion and convulsions. Vitamin B6 deficiency is also linked to increased risk of cancer ⁽²⁰⁾.

There are no adverse effects seen from naturally occurring vitamin B6 from food items. However, very large supplemental doses of pyridoxine is associated with skin lesions and damage to the sensory nerves ⁽²¹⁾. Increased intake of pyridoxine supplements can also reduce milk production in women who are breastfeeding ⁽²²⁾.

Increased doses of pyridoxine have been used for treating premenstrual syndrome and carpal tunnel syndrome. However, these benefits are controversial and there is no concrete evidence to show that pyridoxine supplements are effective in treating these conditions ⁽²³⁾.

Biotin supplements are commonly taken by many people for improving their nails, skin and hair; however, there is no concrete evidence about the benefits of biotin for these.

Vitamin B7 or Biotin is found bonded to proteins or in its free form.

Just like all the B vitamins, Vitamin B7 acts as a coenzyme and is needed for function of the five carboxylases and enzymes that are present in many basic metabolic processes, such as it plays an important role in synthesis of fatty acids, metabolism of amino acid and glucose formation.

There is not much research done as to the presence of Vitamin B7 in food. Animal-sourced foods that are rich in biotin are fish, organ meats, egg yolk, meat and dairy products. Some of the plant sources for biotin are leafy greens, legumes, mushrooms, cauliflower and nuts. The microbiota present in the gut also produces biotin in small quantities.

Vitamin B7 deficiency is not that commonly seen. The risk of deficiency of this vitamin is more in infants who are fed formula which is low in biotin and in individuals who take antiepileptic medications, infants having Leiner’s disease or individuals who are genetically predisposed to Vitamin B7 deficiency ⁽²⁴⁾. Biotin or vitamin B7 deficiency, if not treated, can cause neurological symptoms, like intellectual disability, seizures and lack of muscle coordination ⁽²⁵⁾.

There are no known adverse effects of vitamin B7 at high doses and it does not have a set tolerable upper limit.

There is very less evidence that shows the benefits of biotin and that too in only those people who do not get sufficient amount of this vitamin from their diet. Studies have shown that biotin or Vitamin B7 is beneficial in improving the symptoms in individuals suffering from multiple sclerosis ⁽²⁶⁾. There are also some studies that show that biotin supplements help in improving brittle nails in women; however, better studies are needed to support this benefit ⁽²⁷⁾.

This was first discovered in yeast; however, was later extracted from spinach leaves and this is why this vitamin is given the name as folate or folic acid “leaf” in Latin.

There are many different forms of Vitamin B9 such as:

• Folate: This is a group of vitamin B9 compounds present naturally in foods.
• Folic acid: This is a synthetic form of vitamin B9 that is naturally added to processed foods or is sold in supplement form.
• L-Methylfolate: This form is also known as 5-methyltetrahydrofolate and it is the active form of vitamin B9 present in the body and when used in a supplement form is considered healthier than folic acid.

Vitamin B9 acts as a coenzyme and is much needed for cellular growth, amino acid metabolism and formation of DNA. Vitamin B9 is vital during the phases of rapid cell growth and division, such as occurring in pregnancy and infancy. Vitamin B9 is also required for the formation of white and red blood cells and hence its deficiency can cause anemia.

Some of the good sources of Vitamin B9 are leafy greens, sunflower seeds, asparagus and legumes. Yeast extract spread is extremely rich in vitamin B9 and contains about 3,786 mcg per 100 g.

Deficiency of vitamin B9 rarely occurs on its own and if it is present, then it is often in relation with a poor diet and other nutrient deficiencies. One of the classic symptoms of vitamin B9 deficiency is anemia and it cannot be differentiated from the anemia caused by vitamin B12 deficiency ⁽²⁸⁾. Deficiency of vitamin B9 can also cause birth defects of the neural chord or brain known as neural tube defects ⁽²⁹⁾.

There are no serious adverse effects seen with high intake of vitamin B9.

There is no benefit seen of folic acid supplements in healthy people who are consuming a balanced diet. There are some few studies that suggest Vitamin B9 supplements can help in decreasing the risk of heart disease, improving blood sugar control and can help in mild reduction in depression symptoms ^{(30, 31)}.

This is the only vitamin to have a metallic element that is cobalt in it and hence vitamin B12 is also known as cobalamin.

Vitamin B12 has four primary types, which are cyanocobalamin, hydroxocobalamin, methylcobalamin and adenosylcobalamin ⁽³²⁾. All these forms of vitamin B12 can be found in supplements; however, the most common of them is cyanocobalamin, as it is considered ideal for supplements thanks to its stable nature; however, in food only trace amount of this form is present. The most common naturally occurring type of vitamin B12 is Hydroxocobalamin and it is present in foods that are animal-sourced. Other natural forms, such as adenosylcobalamin and methylcobalamin have become popular in the form of supplements in the past years.

Vitamin B12 acts as a coenzyme and its adequate intake helps in maintaining the function and development of brain, production of red blood cells and neurological function. Vitamin B12 is also needed for converting fat and protein into energy and is vital for DNA synthesis and cell division.

The only dietary sources of vitamin B12 are animal-sourced foods, which consist of meat, eggs, seafood and dairy products. Other rich sources of vitamin B12 consist of types of heart, liver, oysters, octopus, tuna and herring.

Vitamin B12 is naturally stored in the liver that is why any type of deficiency of this vitamin will take a long time for the symptoms to show. Vegetarians and vegans are at greatest risk for vitamin B12 deficiency, as they never or rarely consume animal-sourced foods ⁽³³⁾. Older people can develop vitamin B12 deficiency and can also need regular vitamin B12 injections. Other people who are at risk for developing vitamin B12 deficiency are people who suffer from celiac disease or Crohn’s disease and those who have had weight loss surgery ⁽³⁴⁾. Symptoms of vitamin B12 deficiency consist of health problems, such as loss of appetite, neurological problems, sore tongue and dementia ⁽³⁵⁾.

Only a small part of vitamin B12 is absorbed from the GI tract and the amount that gets absorbed depends on the intrinsic factor production in the stomach. As a result, no adverse effects have been linked with high intake of vitamin B12 in healthy people. The tolerable upper intake level has not been established.

Vitamin B12 supplements are beneficial for those who are deficient or at risk of deficiency. Not much is known about the effects of vitamin B12 supplements in people who follow good diet and get their vitamins from their diets. A small study showed that intake of 1,000 mcg of vitamin B12 in a day helps in improving verbal learning in individuals recovering from strokes; however, more studies are needed ⁽³⁶⁾. For treating cyanide poisoning injections of hydroxocobalamin are given often in conjunction with sodium thiosulfate ⁽³⁷⁾.

The only water-soluble vitamin that does not belong to the vitamin B category is Vitamin C and it is one of the body’s primary antioxidants and is needed for synthesis of collagen.

There are two forms of Vitamin C of which ascorbic acid is the most common.

Vitamin C is important in supporting various important functions of the body, such as:

• Antioxidant for Protection: Antioxidants are used by the body to protect itself from oxidative stress and vitamin C is one of the vital antioxidants ⁽³⁸⁾.
• Collagen Formation: The body is not able to synthesize collagen without vitamin C, which is the main protein of connective tissue. If there is no collagen synthesis due to vitamin C deficiency, then it affects the skin, ligaments, tendons and bones ⁽³⁹⁾.
• Immune Function: Immune cells have increased amounts of vitamin C and when there is infection, there is rapid depletion of vitamin C ⁽⁴⁰⁾.

Vitamin C does not act as a coenzyme; however, it is a cofactor for prolyl hydroxylase, which is an enzyme playing an important role in collagen formation ⁽⁴¹⁾.

Fruits and vegetables are the primary dietary sources of vitamin C. Animal-sourced foods that are cooked do not have any vitamin C; however, some amount of this vitamin can be found in eggs, raw liver, fish, meat and fish roe ⁽⁴²⁾. Drying food items or cooking it significantly reduces the content of vitamin C in them ⁽⁴³⁾.

Vitamin C deficiency is rarely seen in developed countries; however, people who follow restrictive diets or do not eat any vegetables or fruits can have vitamin C deficiency. People who are alcoholics and those having drug addiction problems are at increased risk for vitamin C deficiency. Vitamin C deficiency causes scurvy, which is disease characterized by connective tissue breakdown ⁽⁴⁴⁾. The symptoms of scurvy consist of weakness and fatigue. As there is worsening of this condition, it causes inflamed gums and spotted skin. Advanced stage of scurvy can cause bleeding gums, teeth loss, dry eyes, joint and skin problems, swelling and impaired healing of wounds. Scurvy is life threatening if not treated.

Majority of people are able to tolerate high doses of vitamin C without having any side effects. However, extremely high doses that are more than 3 g of vitamin C per day can cause nausea, diarrhea and abdominal cramps, as only a limited quantity of vitamin C can be absorbed from a single dose.

Not much benefit is seen from vitamin C supplements in people who get their daily requirement of this vitamin from their diet. Vitamin C, however, helps in improving iron absorption from a meal, especially in those who are suffering from iron deficiency ⁽⁴⁵⁾. An analysis of multiple studies showed that vitamin C supplements, about 200 mg per day, can be beneficial in recovering from the common cold ⁽⁴⁶⁾.

The role of B vitamins vary; however, most function as coenzymes in different metabolic pathways. It is easy to get the required amount of all the water-soluble vitamins from a balanced diet. The only B vitamin which is present in large quantities in animal-sourced foods is vitamin B12 resulting in its deficiency. Vegans and vegetarians will need to take its supplements or regular injections.

Except for vitamin B12, the human body does not store these water-soluble B vitamins, hence one needs to follow a healthy and balanced diet everyday to get their required vitamins.

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